Roof window (wood) molding?

Hello everyone,

I am new here and I hope for numerous responses

As part of my volunteer work at my daughter's kindergarten, I am allowed to take care of the following problem:

We have a game room of about 150 m2 in the attic. There are 2 wooden roof windows (Velux?) which are locked for safety reasons. Therefore, it can be assumed that they have rarely or never been ventilated.

Attached you will find a few sample pictures of the windows. To me, it looks like mold, but I would like to have an expert's assessment. The windows are dry from the inside and also feel dry.

The following questions arise in total:

[*]Is it really mold?

[*]If yes, what should be done?

[*]Is this the landlord's responsibility?

I hope for helpful feedback.

Best regards
Baumensch1980

Hi, it's of course hard to say from here. It looks to me like old water damage, so someone left the window open, or something like that. I would measure the wood moisture; if dry, sand it, repaint, or oil/wax. If wet, find the cause. I can't judge the black stuff, but it somehow doesn't look like fungus. Regards

That looks more like moisture damage to me. If the window is not leaking, it could be condensation from the indoor humidity that has formed on the cold window. The window then has a very low thermal insulation value. It would be interesting to know the manufacturing year of the window and the thermal transmittance value (Uw value). For Velux, the type plate can be found at the top right/left of the frame, above the handle strip. Visually, the window could be from the 1990s. If it is condensation and there is no window leakage, this indicates an unusually high indoor humidity combined with low heating performance and inadequate ventilation. The roof may also be insufficiently insulated. This could also be checked in this context.

Hello, we have practically the same situation with the roof window (year 2000), not quite as black. I used to dry my laundry in that room more often... That was not good at all... As wpic already wrote, moisture condenses on the glass during frost (and only then), which then runs down into the wood. The humidity in the room today is 36 percent. Room temperature about 20 degrees. The roof is well insulated. I now always put a small silent fan under the window during frost. That helps very well. The type plate of the window says: Velux GGL 206 3059B, 15 AH 10D. Where can I read the Uw value here? Should I paint the wood after sanding or rather oil it? What else could be done preventively.. Any thermal films on the glass? Best regards Steffi

Hello everyone,

thanks first of all for the answers so far.

Can I use this to "charge" the landlord or is it the tenant's responsibility. As mentioned at the beginning, we are a kindergarten (parents' initiative).

Best regards
Baumensch1980